Thinking ahead to when we are all flying :> , one thing that might limit where we can fly is noise complaints. The increased use of RC drones has led to laws that limit their use, and I’d hate that to happen to PPGs. I don’t know much about noise so I did some googling.

There are 3 main sources of potential noise. Props, Motors and Airframe (or for a ppg the harness, risers, frame etc.) There’s some good research being done on RC quadcopters likeAlex Stoll’s Stanford thesis on RC quadcopter noise. His conclusion showed multi-blade props were quieter, but there seems to be a trade-off between maximum thrust and minimum noise.

Some types of sound are more pleasant than others. Apparently pure, persistent notes are more annoying than varying ‘dirtier’ sounds. Would be great if we could ‘tune’ our rigs like cars or motorbikes.

Does anyone have any ideas on how best to measure and reduce noise levels?

For slow flying ppgs most of the noise comes from the props and the noise is proportional to the prop tip speed together with the shape of the prop tip. The key is to keep the tip speed low (< mach 0.7). Low noise props are continually being developed by various companies e.g http://www.e-props.fr/16/quietestA.php

Seriously, this is a non-issue for me.
From what I see and here in the numerious videos from @pdwhite this thing is so much less noisy than my 2 stroke PPG … I simply don’t care.

In Germany we have to have a license, and we know where we are allowed to fly and where not. (minium 300 Meters above the highest point over congested areas and minimum 150 Meters above non congested Areas).

No one on the ground has the right to bitch or complain about any noise generated by an aircraft respecting these rules.

And you simply can not bypass the laws of physics and earodynamics. If the prop moves air, there will be noise.

etienne, I agree quiet flight is more of a ‘nice to have’ issue than a ‘must have’.
For example, if a 3-blade prop was quieter, but meant the frame couldn’t fold like PDWhite’s clever design, then I’d just be noisy.

I’m mostly asking because I’m curious, so JohnH’s comment and link were very interesting.
I wonder at what height a PPG becomes inaudible? How high would you have to be flying so the average person won’t hear you at all? (Maybe that’s why Germany has the 150m height limit).